1. Field of the Invention
The present invention relates to a switching regulator and particularly to switching regulators with a network of a coil, a capacitance and a diode, which are connected in a ring-like way.
2. Description of the Related Art
FIG. 4 shows a known down converter with a simple switch, such as, for example, shown in “Halbleiter-schaltungstechnik” U. Tietze, C. H. Schenk, Springer-Verlag, 9. Auflage, 1989, illustration 18.37 on page 564. The down converter in FIG. 4 comprises a ring-like circuit with a coil 400, a capacitor 402 and a diode 404. Further, the down converter or switching regulator, respectively, in FIG. 4 comprises a charging switch 406 as well as a control not shown in FIG. 4, which is formed to control the charging switch 406 such that the output voltage of the switching regulator, indicated by USR in FIG. 4, is maintained on a defined level or in a range around the defined level, respectively.
The circuit shown in FIG. 4 comprises a determined number of nodes, which will be discussed below. A pole of an input voltage source U0 is connected to a first input node 410 of the circuit, while another potential of the input source U0 is connected to a second input node 412. The second input node 412 is typically the ground node. A first output node 414 is also referred to as first output rail or positive output rail, while a second output node 416 is also referred to as second output rail or negative output rail, respectively, when the convention shown in FIG. 4 is used for the output voltage of the switching regulator USR. On the one hand, the switch 406 is connected between the first input node 410 and a first intermediate node 418. Further, the diode 404 is connected between the first intermediate node 418 and the second input node 412, such that the anode of the diode is connected to the second input node 412, while the cathode of the diode is connected to the first input node 418. Further, as shown in FIG. 4, the capacitor 402 is connected between the first output node 414 and the second output node 416. According to the configuration of the network of diode, coil and capacitor shown in FIG. 4, the coil is connected between the first intermediate node 418 and the first output node 414.
Below, the functionality of the circuit shown in FIG. 4 will be discussed. As long as the switch 406 is closed, UD is equal to the negative input voltage U0. If it opens, the inductor current IL maintains its direction, and the amount of UD sinks, until the diode becomes conductive, which means to about 0 potential. The time curve of the coil current results from the law of induction, according to which the voltage at the coil is equal to the product of inductance L of the coil and the derivation of the coil current according to time. During the switch-on time, which means when the input voltage U0 is applied to the diode 404, the voltage U0−USR is applied to the inductor. During the switch-off time taus of the switch 406, the voltage UL=−USR is applied to the inductor. Therefore, an amount of current change ΔIL results, which is as follows:ΔIL=1/L·(−USR)·Δtaus=1/L (U0−USR)teinFrom this balance, the output voltage can be calculated again, which is defined as follows:USR=[tein/(tein+taus)]·U0=tein/T·U0=p·U0.In the previous equation, T=tein+taus=1/F is the oscillation period and p=tein/T is the so called duty cycle. As expected, it can be seen that the arithmetic average of UD results as output voltage. Typically, the inductance L of the coil 400 is chosen such that the minimum current is not undershot, as is known in the art. Further, it is known that by increasing the clock frequency, the inductance can be reduced. Further, with too high frequencies, the effort for the switching transistor and the control circuit increases. Additionally, dynamic switching losses increase in proportion to the frequency.
The capacitor 402 and the inductor 400 determine the ripple of the output voltage. Generating the switching signal for switching the charging transistor 406 is usually performed by a pulse width modulator and a regulator with voltage reference. In particular, a reference voltage providing a set value is supplied to a subtracter, to which the current output voltage USR is also supplied as actual value. The output signal of the subtracter is supplied to a variable gain amplifier, feeding a comparator, to which, on the other hand, a signal generated by a saw tooth generator is supplied. The output signal of the comparator is the control signal for the switch 406 in FIG. 4. The variable gain amplifier is typically a PI variable gain amplifier. The same increases its output signal for so long until the difference at the output of the subtracter becomes 0, which means until the output voltage USR is equal to the set output voltage. Typical ranges for dimensioning the coil are in the millihenry range (e.g. 2.7 mH), while typical values for capacitors are in the three-digit micro Farad range (e.g. 100 μF.), when switching frequencies in the range of 50 kHz are used.
Switching regulators shown in FIG. 4 are to provide a suitable voltage supply to a subsequently connected circuit, such as an ASIC. The voltage supply consists normally of one or several constant direct voltages of, for example, +5 V or ±15 V. Frequently, the same is not available in the desired form from the start and has to be generated first by, for example, a switching regulator shown in FIG. 8 that can be supplemented by a downstream linear regulator to remove the ripples of the output voltage. Usually, a rectifier is at the input side of the switching regulator shown in FIG. 8 which generates the input voltage U0 from the alternating current or three-phase current net (230 V or 400 V), respectively, of the power station.
Thus, in deviation from the switching regulator shown in FIG. 4, other regulators exist, with a transformer, a rectifier, a smoothing capacitor and possibly a linear regulator for voltage stabilization. However, the transformer is difficult to produce and thus expensive. Further, it requires a lot of space. A further disadvantage of the transformer is its frequency-depending working range. This is, for example, limited to the network frequency of 50 Hz or 60 Hz, respectively. If the frequency deviates, this also causes a deviation of the output voltage of the transformer. The voltage transfer does not work with a direct voltage at the input.
If the transformer is omitted and only rectifier, smoothing capacitor and linear regulator are used, a lot of energy in the form of heat is lost. Additionally, sufficient cooling of the linear regulator has to be provided, which is again very expensive and requires space. All this is avoided by using a switching regulator instead of the linear regulator, as illustrated with regard to FIG. 4. By the significantly better efficiency, little energy in the form of heat is lost and thus the effort for the cooling is significantly lower. As has already been discussed, the switching regulator requires an inductor (the inductance 400 in FIG. 4), which is relatively expensive in the production. However, the same has only one winding and is thus simpler to produce than a transformer having two windings. Above that, the inductor can be minimized by selecting a higher operating frequency, which also works for transformers.
Many known switching network parts, such as the switching network part shown in FIG. 4, are problematical in some regard. Normally, the input voltage range is limited to a ratio of UE,max/UE,min≦5, which can be seen from catalogs of different providers. This range is too low for some applications and should be increased to a ratio of about 20:1.
The voltage supply of the regulator itself is either performed via a separate voltage source or is generated from the input voltage, which means an additional voltage regulator and thus additional effort.
Further, for a flexible usage, it is intended to be able to select the input voltage significantly higher than the maximum allowable operating voltage of the regulator itself, without using additional voltage regulators for generating this operating voltage.
Additionally, when applying the input voltage, a possibly fast controlled starting of the switching regulator should be ensured. This so called starting-delay should be as small as possible, particularly for time-critical applications.
It is a particular disadvantage of the switching regulator concept shown in FIG. 4 that the signal for controlling the switch 406 has to be generated externally. Thus, on the one hand, the timing of the signal is determined by regulating the output voltage USR by an externally supplied regulator. Further, the signal actually applied to the switch, which can, for example, be a transistor, which will be the gate voltage of the transistor in the case of the transistor, is again generated externally in a switching regulator, which again results in a voltage converter, to apply a control signal with the correct potential to the switch. As has been discussed, the signal directly applied to the switch 406 is thus either provided externally or generated from the input voltage U0.
DE 199 46 025, DE 197 00 100 C2, DE 195 07 553 A1 or DE 197 06 491 A1 disclose switching regulators operating based on the basic block diagram shown in FIG. 4, wherein depending on the embodiment, the coil 400 is either connected between the first intermediate node 418 and the first output node 414, as shown in FIG. 4, or alternatively, between the second input node 412 and the second output node 416. The control voltage for the switch 406, which can be designed as transistor, is determined by the regulator determining the timing of the switch 406 or generated externally. This causes additional switching effort, which means additional costs with regard to design, testing and production. Additional costs are particular disadvantageous since switching regulators, particularly when they are provided within lamps or also designed fully integrated with an integrated circuit to be supplied, increase the price of the final product and particularly occur in chip applications where the chip area is a criterion, due to the increased chip area consumption.